Exploring Human Impacts And Climate Change Using Fossils

[Doctor Mud]

Hi all,

I've been a member here for a while now and posted mostly about what I do with fossils for fun. This is what got me started as a kid interested in this whole thing. Splitting open a rock and being the first human to see the remains of a long-dead life form. I always knew I wanted to be a palaeontologist, but imagined myself as the more "traditional" palaeontologist out in the field probably extracting large vertebrate fossils from hard rock laid down millions of years ago.

I thought I would start this thread to share some of my work with fossils that I do for a living. This is a little bit different to most of what is posted on here, but I thought some folks might enjoy it. I'm basically a paleoecologist dealing with younger deposits, so many of the principles are the same as paleontology and paleoecology in "deeper" time. I think we just "pretend" to have more precision!

My work focuses mainly on environmental change during the Quaternary or about the last 2.6 million years. A lot of people study this time period since the Earth was pretty much in the same configuration as it is today (placement of the continents) and so we might be able to predict the future by understanding the past.

I mainly work with lake and bog sediments as these are excellent archives of environmental change. Layers of mud slowly build up over time and incorporate all sorts of fossils that can tell us about the conditions in the lake or bog (e.g. water quality), vegetation and fires in the catchment (via fossil pollen and charcoal). I'm interested in how humans modify ecosystems through deforestation and agriculture and also long term climate change.

I thought I would share some reports and pics of field trips - some recent ones and some still to come and share and describe the methods and results and what they actually mean.

Watch this space!

Edited July 7, 2015 by Doctor Mud

[Raggedy Man]

[Doctor Mud]

I thought I would start with a recent project that has been wrapping up. This will give you an idea of how things work.

I look at environmental change on different timescales and through the lens of wetlands. I look at human impacts on forests and wetlands over the last 12,000 years (when humans transitioned from hunter gatherers to agriculture) and climate change over the last 2.6 million years (the Quaternary period).

I work on wetlands because they are good natural archives for environmental change and because they are sites of environmental significance themselves. They support biodiversity, provide ecosystem services, food and often drinking water.

This project from the New England Tablelands in New South Wales in Australia gives you an example of a "typical" project. The New England Tablelands are an area of high elevation (> 1300 m) in northern New South Wales in eastern Australia.

The New England Tablelands

There are numerous wetlands in this area that are locally known as lagoons. A couple of these shallow wetlands caught our eye since a previous study suggested that these had existed since the last ice age or for 20,000 years or so. One (Little Llangothlin Lagoon) is a special wetland known as a Ramsar wetland which means it is on a list of globally important wetlands that experience an elevated level of protection.

Llangothlin and Little Llangothlin lagoons

The jury is still out as to how these actually formed, but various theories have been offered including lava flows damming old valleys millions of years ago.

Little Llangothlin Lagoon

I was part of a team looking at the environment in Australia during the last ice age and since these wetlands were around then they seemed like perfect sites to provide a window into the environment at that time. We also planned to establish the natural conditions in the wetland prior to human impacts to aid management of Little Llangothlin.

"Fossil hunting" is a little different in this case as we take core samples from wetlands and look at fossils preserved in the layers of mud. Layer by layer we build up a story of how the environment has changed through time.

[Doctor Mud]

The backstory of Little Llangothlin:

Apart from being a Ramsar wetland, Little Llangothlin is also a special site in terms of Australian history.

Previous work suggested that illegal settlers left Sydney as early as 1800 AD and cleared the land in this area pretty much causing most of the soil in the catchment to be eroded into the wetlands. Aboriginals have been in Australia for at least 50,000 years but given the high altitude of this area, and the bitter winters (well for Australia anyway ) Aboriginal populations and impacts were low.

For those of you that don't know, Sydney was a penal colony and settlers weren't officially allowed to leave the area around Sydney (the limits of location) until sanctions were lifted in 1840 AD.

The evidence for this "environmental crime" revolves around a layer of eroded soil that previous workers found buried in the lagoon.

But - were they correct?

That's all for this installment. I will follow up next time with showing you how we cored Little Llangothlin Lagoon and how we reconstructed its history over the last 20,000 years from the environment during the last ice age to the arrival of European agriculture in the 19th century using fossils. Stay tuned for surprises including the tale told by fossil flies, radioactive lead and how aboveground nuclear tests can help us to date environmental change.

Edited July 8, 2015 by Doctor Mud

[Plax]

very interesting! Looking forward to future installments

[the tatter]

This is fascinating, I want to know more please.

[Doctor Mud]

Thanks guys. I'm glad you are enjoying it.

I'll continue the story tomorrow when I have access to my photos and data.

[Ludwigia]

I'm with you too Thanks for sharing on this important subject. Sounds like a fascinating career.

[Doctor Mud]

So how do you go about taking core samples?

Well there are two main methods. For a lake like this we use what is known as a gravity corer for looking at the shallow sediments and some sort of corer that uses a bit more force like a Livingstone corer that can get to the deeper sediments.

A gravity corer is just what it says on the tin. It just uses gravity and is a glorified tube that sinks into the mud. There is also a spring loaded cap that creates suction so when you lift the tube out the mud stays in. Think of putting a straw into a glass of water and putting your finger over the top to keep the water in.

Another great gravity core! Note the black plunger on top which creates the suction to keep in all the mud when you pull out the tube.

This core is from a lake in London, Ontario, Canada. That core represents about 100 years of accumulation.

For those interested in how it works. A figure from Woodward & Sloss (2013). The unit is lowered from a boat (1) and is allowed to sink into the mud (2). The suction cup on top is triggered by dropping down a "messenger" (3) and then the how thing can be lifted up with its muddy treasure!

You then take real care to keep this vertical and sub-sample the core in the field. This way you don't loose all the sloppy mud on the top. It is common for the shallow layers of mud to be sloppy. Laying down the core to transport it to the lab would result in a sloppy mess!

We extrude the mud on site using a special vertical extruder that can extrude layers at set intervals, usually 0.5 - 1 cm. A layers is squeezed out and then put in a sterile labelled sample baggy for later analysis. This is mud from a lake in western Ireland.

Ta da! Here is one of many gravity cores we took from Little Llangothlin. Its like a little snapshot of the surface of the lake bottom. The top sediments, weeds and even lake water have been sampled. The mud here took roughly 300 years to accumulate.

Reference:

Chapter: Woodward C.A., and Sloss C.R. (2013) Coring and Augering. In: John F. Shroder (ed.) Treatise on Geomorphology, Volume 14, pp. 119-137. San Diego: Academic Press

Edited July 12, 2015 by Doctor Mud

[Doctor Mud]

To get at those deeper sediments we use something that requires a bit more brute force. Mechanised rigs can be used, but these are often not portable and you would be amazed at what can be achieved with human power!

A common corer used to sample deeper mud is called a Livingstone corer named after its inventor Daniel Livingstone https://en.wikipedia.org/wiki/Daniel_A._Livingstone. Its is also a glorified tube, but instead of settling into the mud under the power of gravity, it is pushed in. To get deeper, series of extension rods can be added to the handle. There is also a piston inside the barrel that helps to "suck up" the mud and prevents plugging. Plugging is when there is too much friction for the mud to enter the core tube.

Diagram of a Livingstone corer from Woodward and Sloss (2013). A. shows a cross section of the corer (A) The core tube is 5 cm diameter. B. shows how it works. You push the core tube into the mud and keep the cable tight to create suction (1 & 2) until the core tube is full (3). You then lift out the full barrel and extrude out the mud carefully into something like a PVC half-pipe (usually drain-pipe cut in half). You can then go back to the same hole and add an extension rod to go deeper. The depth of core you can collect is limited by how soft the sediment is. I've gone down to 10 m with this method.

Here's a bunch of us coring Little Llangothlin with a Livingstone. I'm the one partially obscured by the guy in the red t-shirt. You can see the extension rods we are using to go deeper. The white pipe sticking out of the water is a marker post left by the original researchers who cored the lake back in 1995. Here we are taking a replicate to test their results.

Edited July 12, 2015 by Doctor Mud

[Auspex]

This is an excellent primer/short course on the art of this science! I am very grateful that you are taking the time to present it.

[Doctor Mud]

I'm with you too Thanks for sharing on this important subject. Sounds like a fascinating career.

Thanks Ludwigia. Glad you are enjoying it.

[Doctor Mud]

This is an excellent primer/short course on the art of this science! I am very grateful that you are taking the time to present it.

Thanks Auspex. I have received so much information from TFF that it is only fair that I put a little back. Its a little different from the mostly "hard rock" paleontology on here, but based on fossils none the less

[Doctor Mud]

Well - I can't get this far into the topic and not talk about fossils can I??

Well as Monty Python would say - now for something completely different. Fossil flies. These little guys were one of the keys to unlocking the history of Little Llangothlin.

I bet there are many keen fisherman/people on here and you are probably not a stranger to the blood worm. Many of you might have goldfish and have fed them bloodworms that often come in frozen cakes that you pop in the tank.

These are not true worms, but the larvae of a type of fly known as a non-biting midge or chironomid. You may have met non-biting midges in your travels. You would know as (as the name suggests) they don't feed on your blood. You might see clouds of flies near streams or lakes and they aren't interested in feeding on you. They are closely related to biting midges and mosquitoes, but are not sent to torture people in the outdoors.

Swarms of non-biting midges above Lake Malawi in Africa. Unlike mosquitoes, non-biting midges (chironomids) emerge only to mate and may only live for one day.

This may sound confusing when the larvae are called blood worms. But the life cycle of the non-biting midge is like a Mosquito and there is an adult stage (the fly) and a juvenile stage (the larvae). The larvae live in water and the name "blood worm" refers to the fact that some species actually have a type of haemoglobin that helps them to regulate their oxygen supply and survive low oxygen conditions. Haemoglobin is red (it's in your blood as well) and some of the larvae are blood red.

A living blood worm or chironomid larva from Little Llangothlin Lagoon. The larvae live in water. Some live attached to aquatic plants and some even live in burrows in the lake bottom. They feed on all sorts of things including plankton, diatoms (algae), small insects and each other! Like a mosquito, the larva will eventually morph into a pupa and swim to the surface and emerge as a fly.

Edited July 12, 2015 by Doctor Mud

[Doctor Mud]

Non-biting midge larvae or chironomid fossils are a really useful tool in paleoecology, or the study of environmental change in wetlands.

Their bodies are fleshy, but they have a little head made of chitin, which is what the armour or exoskeleton of insects and crustaceans is made of. This head fossilises and can usually be identified to genus and sometimes species........by looking at their teeth!!

Far left. A blood worm or chironomid larva. You can just make out the head or head-capsule (inside red square). Top right is an SEM of a chironomid head. Bottom right shows chironomid heads extracted from lake sediment ready to be counted and identified. These guys are from a brackish coastal lake in New Zealand. There can be as many as thousands of these heads in one teaspoon of lake mud! There can also be dozens of species of non-biting midge living in the same wetland or lake!

There are thousands of species of chironomid, living in lakes, streams, thermal pools, melt-water on glaciers and water collected in pitcher plants. The important thing for paleoecologists is that different species like to live in different environments. For example. The 'blood worms' (classified as tribe chironomini) can survive low oxygen conditions and are normally more abundant in lakes that have experienced pollution by nutrients (known as eutrophication). You can tell the species apart by looking at their teeth or menta.

Examples of chironomid "teeth" or menta from different fossil genera. These are all less than a mm across. The genus on the top left (Harrisius spp.) only lives in burrows on submerged wood, while the genus on the bottom left (Parochlus spp.) is common in cold mountain streams or very cold lakes. The genus on the bottom right (Polypedilum spp.) only lives in warmer lakes and we see this disappear in some records from lakes during ice ages and re-appear afterwards.

My avatar is actually a midge larval head and you can see the teeth or mentum at the bottom with the mandibles curved into the mouth. This head would maybe be a mm across.

Chironomids are an example of what we call a paleo proxy. It is something that can be extracted from a natural archive (such as lake sediments) whose ecology or behaviour can tell us about past environmental conditions. First we need to understand the ecology of the species and we can use this to understand the fossil record. Other examples of paleo-proxies in wetlands include pollen, diatoms (algae with glass "skeletons") and cladocera (aquatic "fleas"). We can even use the chemistry of the mud to tell us about past conditions.

Edited July 12, 2015 by Doctor Mud